In the prior art, there is known a game system which can generate an image viewable from a given viewpoint in an object space that is a virtual three-dimensional space. Such a game system is very popular as a system which can realize a so-called virtual reality. If the game system is used to enjoy a roll-playing game, a player can enjoy the game by controlling a character (or object) to move on a map within the object space such that the character will fight against an enemy character, dialogue with another character and visit various cities.
In the game system, an object representing a character or the like is usually formed by a plurality of polygons (or primitive surfaces). The object (or model) formed by the polygons is arranged within the object space and subjected to the geometry processing (or three-dimension computation) for generating an image viewable from a virtual camera (or viewpoint). This enables a consistent game image to be generated even when this object is viewed through the virtual camera in various directions.
However, the game image so generated is mathematically correct, but cannot sufficiently hit the feeling of the player.
For example, the outline (edge line) of the object formed by the polygons is always formed by a line having its invariable thickness without dependence on the shape of the object, the direction in which the object is viewed and so on. If a character in an animated cartoon is to be represented by the object formed by the polygons, therefore, the image thereof having an atmosphere unfamiliar to the general public will be generated since it has a monotonous outline.